<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>首页</title>
</head>
<body>

<div style="width: 70%;height: 150px; border: 2px solid green;">
    {% block header %}
    <span>this is header</span>
    {% endblock %}
</div>

<div style="width: 50%;height: 250px;border: 2px solid  red;" >
    {% block content %}
         <span> this is content</span>
    {% endblock %}
</div>

<div style="width: 70%;height: 100px;border: 3px solid blue;">
    {% block footer %}
        <span>
        this is footer;
        </span>
    {% endblock %}
</div>
</body>
</html>